The present invention relates to a method for the fractionation of molasses using a chromatographic simulated moving bed system in which the liquid flow is effected in a single direction in a system comprising at least two chromatographic partial packing material beds. Fractionation of molasses denotes fractionation of various vegetable-derived by-products of the food and fermenting industries, such as beet and cane molasses, stillage, vinasse, slop, wood molasses, corn steep water, wheat, barley and corn molasses (hydrolyzed C starch). In the method of the invention, the product or products are recovered during a multi-step sequence comprising the following phases: feeding phase of molasses, eluting phase and recycling phase.
The liquid present in the partial packing material beds with their dry solids profile is recycled in the recycling phase in a loop comprising one, two or several partial packing material beds.
These phases are employed to form sequences comprising several process steps. In accordance with the invention, a sequence preferably comprises five to ten steps. A step comprises for example
a molasses feeding phase and/or feeding of an eluant liquid and recovery of the product or products, or
an eluting phase with recovery of a product or products, or
recycling phase and eluting phase with recovery of a product or products, or
two or more recycling phases.
Sequences comprising said steps are repeated five to seven times to reach an equilibrium.
Typically from three to twelve, preferably three to six chromatographic partial packing material beds are employed. A loop may comprise one, two or several partial packing material beds. Strongly acid cation exchange resin is preferably used as the column packing material.
The simulated moving bed system has been developed and introduced by UOP (United Oil Products), U.S.A., at the beginning of the 1960""s, initially for petrochemical applications (U.S. Pat. No. 2,985,589). Today several simulated moving bed methods for a number of different applications are known (U.S. Pat. Nos. 3,706,812, 4,157,267, 4,267,054, 4,293,346, 4,312,678, 4,313,015, 4,332,623, 4,359,430, 4,379,751, 4,402,832, 4,412,866, 4,461,649, 4,533,398 and 5,127,957, and published European application 0,279,946).
The simulated moving bed system enables separating performances that are many times higher, and lower dilution of the products (consumption of eluant) than in the batch method.
The simulated moving bed method is either continuous or sequential.
In a continuous simulated moving bed method, all flows are continuous. These flows are: feeding of feed solution and eluant liquid, recycling of liquid mixture and recovery of products. (usually only two). The flow rate for these flows may be adjusted in accordance with the separation goals (yield, purity, capacity). Normally, 8 to 20 partial packing material beds are combined into a single loop. In accordance with the above-mentioned U.S. Pat. No. 4,402,832, the recycling phases have been applied to the recycling of dilute fractions. The feed and product recovery points are shifted cyclically in the downstream direction. On account of the feed of eluant liquid and feed solution (and on account of recovery of products) and the flow through the packing material bed, a dry solids profile is formed. Ingredients having a lower migration rate in the packing bed are concentrated at the downstream end of the dry solids profile, and respectively ingredients having a higher migration rate at the upstream end. Feeding points for feeding solution and eluant liquid and recovery points for product or products are shifted gradually at substantially the same rate at which the dry solids profile moves in the bed. The product or products are recovered substantially from the upstream and downstream end of the dry solids profile, and the feed solution is fed approximately to the maximum point of the dry solids profile and the eluant liquid approximately to the minimum point of the dry solids profile. Part of the separated product fraction is recycled on account of the continuous cyclic flow and as only part of the dry solids profile is removed from the packing material bed.
The cyclical shifting of the feed and recovery points is performed by using feed and recovery valves disposed along the packing material bed at the upstream and downstream end of each partial packing material bed. If it is desired to recover product fractions of high purity, short phase times and a plurality of partial packing material beds must be employed (the apparatus has corresponding valves and feed and recovery equipment).
In a sequential simulated moving bed method, not all flows are continuous. In a sequential simulated moving bed method the flows are: feeding of feed solution and eluant liquid, recycling of liquid mixture and recovery of products (two to four or more products; e.g. betaine as a third fraction in beet molasses separation and monosaccharides in cane sugar separation). The flow rate and the volumes of the different feeds and product fractions may be adjusted in accordance with the separation goals (yield, purity, capacity). The method comprises three basic phases: feeding, elution, and recycling. During the feed phase, a feed solution and possibly also an eluant liquid is fed into predetermined partial packing material beds, and simultaneously two or even three product fractions are recovered. During the eluting phase, eluant liquid is fed into a predetermined partial packing material bed, and during said phases one or even two product fractions are recovered in addition to the residue. During the recycling phase, no feed solution or eluant liquid is fed into the partial packing material beds and no products are recovered.
Finnish Patent Application 882740 (U.S. Pat. No. 5,127,957) discloses a method for recovery of betaine and sucrose from beet molasses using a sequential simulated moving bed method, the chromatographic system therein comprising at least three chromatographic partial packing material beds connected in series and adapted for the flow of liquids in a single direction in partial packing material beds, in which method betaine and sucrose are separated during the same sequence comprising:
molasses feeding phase, in which a molasses feed solution is fed into one of said partial packing material beds and in which eluant water is fed substantially simultaneously into another partial packing material bed,
feeding phase of eluant water, and
recycling phase,
these phases being repeated either once or several times during the sequence.
A novel sequential simulated moving bed method has now been developed, which is particularly suitable for the fractionation of molasses. The novel method yields a purer sucrose solution with a better yield and/or capacity.